Interpretive Summary: The western cherry fruit fly damages sweet cherry fruit and is a major quarantine pest of cherries in the western U.S. Determining environmental requirements of the fly is needed to help predict whether it can establish in high numbers where cherries are grown. Personnel at the USDA-ARS Yakima Agricultural Research Laboratory in Wapato, WA tested the effects of media types and moisture on the ability of fly pupae to survive and emerge as adults. It was found that dry loam soil was detrimental for fly health and for pupae, causing higher deformities or mortality than moist soil. This result suggests that dry loam soils could suppress fly populations, although other environmental factors also must affect fly population sizes.

Technical Abstract:
Adult emergence and pupal mortality of tephritid flies depend on soil type and/or moisture. In this study, the influence of media type and moisture on adult development and pupal mortality in western cherry fruit fly, Rhagoletis indifferens Curran, was assessed. Inside sealed containers, a higher (mean) percent of flies that emerged from dry loam was deformed (44.2% or 84.4%) than flies from 16% moist loam and dry and 16% moist lab soil (peat moss-sand mix) (0–14.9%). Percent of flies deformed from dry sand (22.1% or 49.5%) was greater than from 16% moist sand and dry and 16% moist peat moss (0–10.5%). Percents of flies deformed from 8% moist loam, lab soil, sand, and peat moss (0–5.8%) did not differ. Pupae suffered higher mortality at 7 and 14 d after larvae were dropped onto dry loam and dry sand (68.2–94.0%) than dry lab soil and dry peat moss (3.0–53.0%); however, respective mortalities at 21 and 28 d were similar (81.3–96.0 versus 64.7–97.9%). Pupal mortality in 8% and 16% moist media was lower (0.5–40.3%) than in dry media. In outdoor tests, pupal mortality was also higher in dry loam than other dry media. In nature, 60.9% of pupae in dry sandy loams were dead. Results suggest R. indifferens has not yet evolved to fully cope with dry soils, even though the fly is abundant in dry habitats, implying multiple environmental factors could reduce apparent negative effects of dry soils on fly numbers in nature.